1. Field of the Invention
This invention relates to a laser beam scanner and a photographic printer using the laser beam scanner as an exposure apparatus for exposing a photographic paper.
2. Description of the Related Art
A conventional a photographic printer using a laser beam scanner as an exposure apparatus, for example, shown in Publication Gazette of Japanese Patent application Hei 11-84293 is described. In the photographic printer, a photographic paper is conveyed in a predetermined direction (hereupon, the direction is called xe2x80x9csub-scanning directionxe2x80x9d) at a predetermined constant speed. Laser beams corresponding to three primary colors or complementary colors thereof are scanned on a photo-sensitive surface of the photographic paper in a main scanning direction perpendicular to the sub-scanning direction. Intensities of the laser beams are respectively modulated for corresponding to an image data which is taken by scanning a film or photograph by an image pickup scanner or directly taken by a digital camera, or the like.
In the equipment using the laser beam scanner as an exposure unit, photo sensors such as photo diodes are generally provided in optical paths of the laser beams for sensing intensities of the laser beams. The sensed results of the photo sensors are fed back to drivers of the laser light sources, so that driving signals of the laser light sources are compensated for maintaining the intensities of the laser beams in a predetermined range.
In the photographic printer, it is required to reduce the variation of the intensity of the laser beams less than xc2x11% for realizing proper quality of the printed photograph. On the other hand, since the laser light sources are easily affected by environmental conditions, or the like, it is difficult to reduce the variation of the intensities of the laser beams less than xc2x13% even when the sensed results of the actual intensity of the laser beams are fed back. Thus, the variation of the intensity of the laser beam causes a variation of the density in a monochrome, and causes a variation of tint in a color photograph. Furthermore, when the same photographs are reprinted by using the same film in future, there is a possibility that the tint of the reprinted photographs will be different from the original print.
An object of the present invention is to provide a laser beam scanner and a photographic printer using the same, by which the variation of the intensities of the laser beams is reduced less thanxc2x11% so that the quality of the printed photograph can be maintained or improved.
A laser beam scanner in accordance with the present invention comprises at least one set of a laser light source for emitting a laser light beam, a modulator for modulating an intensity of a laser beam passing therethrough, and a driver for driving the modulator by using optical modulation data. A photo sensor is disposed on an optical path of the laser beam passing through the modulator for sensing an intensity of the laser beam passing through the modulator. The driver includes a renewable lookup table for memorizing a set of optical modulation data corresponding to respective stages of gradation of image data, and a compensator for compensating the optical modulation data in the lookup table by using the intensity of the laser beam sensed by the photo sensor when the intensity of the laser beam is discrepant from a predetermined initial value.
By such a configuration, even when the intensity of the laser beam passing through the modulator is discrepant from the standard value due to the variation of the intensity of the laser beam emitted from the laser light source, the optical modulation data used for controlling the modulator are compensated so that the actual intensity of the laser beam passing through the modulator coincides with or approaches to the standard value. Thus, the variation of the intensity of the laser beam passing through the modulator is maintained in a predetermined range less than that of the laser beam emitted from the laser light source.
A photographic printer in accordance with the present invention includes the above-mentioned laser beam scanner, a conveyor for conveying a photographic paper to the predetermined scanning plane of the above-mentioned laser beam scanner and a developer for developing a latent image exposed on the photographic paper by the laser beam scanner.
By using the above-mentioned laser beam scanner as an exposure unit, the variation of the intensity of the laser beam used for exposing a latent image on a photographic paper can be restricted in a very narrow range, so that the quality of the printed photograph can be increased.